The output beam of a laser diode typically diverges a t a small angel (5.degree.-15.degree.) in one axis, the "slow" axis, and at a much larger angle (25.degree.-80.degree.) in the other, or "fast" axis, and it is desirable to correct the beam so as to provide an angularly symmetric beam.
In U.S. Pat. No. 5,171,224, titled "Microoptic Lenses", filed May 10, 1991, there are taught a number of configurations including cylindrical microlenses, although not of the graded-index type. Some of these configurations include lenses which change the divergence of an entering beam in the fast axis to a different divergence; in some cases the output beam is collimated; and in cases the angle of the fast axis is reduced to match the angle of the slow axis, i.e., the beam is circularized.
In recent years a new type of cylindrical microlens has come into use, a graded index lens, in which the index of refraction is graded in a radially symmetric manner. This resultant graded-index lens will affect the propagation of one axis of a light beam incident on the microlens in a direction perpendicular to the longitudinal axis of the lens. Such a lens is described in various publications by Sead Doric, including product literature and Canadian Patent Application No.: 2,135,128 (laid open for inspection), entitled: "NONFULL APERTURE LUNEBERG-TYPE LENS WITH A GRADED INDEX CORE AND HOMOGENOUS CLADDING, METHOD FOR FORMING THEREOF, AND HIGH NUMERICAL APERTURE LASER DIODE ASSEMBLY" (hereafter the '128 reference.).
In each of the Doric references of which the present inventor is aware (including the '128 reference), the graded-index cylindrical microlenses are always used to collimate the fast axis of the incident laser beams.
The present inventor is also aware of a "posting" on the Internet, in which a graded-index lens is used to reimage, rather than collimate, the beam on the slow axis, but not in the fast axis.